The present invention relates to an auxiliary drive and an automobile equipped with the same.
As disclosed in JP-A-9-9414 specification, conventional automobiles equipped with an auxiliary drive, for example, hybrid automobiles have an engine and a motor, and transmit power from at least one of them to an output shaft, and change speed through a multi-speed automatic transmission disposed between the engine and the output shaft. The conventional hybrid automobile comprises an electric power source that provides electric power to the motor and receives regenerative power returned from the motor which acts as a generator, and remaining-amount detection means for detecting remaining electric power capacity of the electric power source. In the convention hybrid automobiles, a shift point which determines steps of the multi-speed automatic transmission is moved in a direction to increase range of low speed in accordance with degree of decrement of the remaining electric power capacity detected by the remaining-amount detection means.
In the above-described specification, there is description that it is possible to increase the rotation of the engine as a whole to increase the regenerative electric power of the motor acting as a generator. However, since according to the above-described prior art, movement of the shift points which determine steps of the multi-speed automatic transmission is depending on degree of decrement of the remaining electric power capacity, there is possibility that a shift to a lower gear may be made during deceleration running. In such a case, the rotational speed of the engine increases to result in increased friction torque, and therefore, there is possibility that engine braking force in excess of braking force demanded by a driver occurs.
In a structure in which a motor is placed on an output side of an engine, a multi-speed automatic transmission equipped with a torque converter is placed subsequent to the motor, and an output shaft is placed subsequent to the multi-speed automatic transmission, if the above-described unexpected shift to a lower gear is made during deceleration running, rotational speed of the torque converter increases on the side of the multi-speed automatic transmission, increasing engine braking force temporarily. Therefore, there is possibility that a driver feels a shock depending on running state.
Furthermore, at the time of moving shift points which determine steps of the multi-speed automatic transmission, it is necessary to move the shift points of both up-shift (speed change decreasing the gear ratio) and down-shift (speed change increasing the gear ratio). This makes the timing of an up-shift during accelerated running in dependant on degree of decrement in remaining power capacity, which may cause the driver to experience an uncomfortable feeling of changing speed.
The above-described circumstances are not desirable for the operability of automobiles and the amenity.
The present invention has been achieved to solve at least one of the above problems. An object of the invention is to provide an auxiliary drive which can be retrofitted to existing automobiles easily and can improve the operability, comfortableness, and fuel economy of the automobiles as well as to provide an automobile equipped with the auxiliary drive.
To attain the above object, an auxiliary drive and an automobile equipped with the auxiliary drive according to the present invention comprise a rotating electric machine connected to an engine and functioning at least as a generator, speed change means disposed between the engine and a wheel axle and means for controlling gear ratio or shift points of the speed change means.
More preferably, the auxiliary drive and the automobile equipped with the auxiliary drive according to the present invention comprise a rotating electric machine connected to an engine and functioning at least as a generator, speed change means disposed between the engine and a wheel axle, demanded braking force detection means for detecting braking force demanded by a driver, engine braking force calculation means for calculating engine braking force and regenerative braking force calculation means for calculating regenerative braking force produced by regenerative power generation of the rotating electric machine, wherein gear ratio or shift point of the speed change means is controlled based on information from the demanded braking force detection means, the engine braking force calculation means and the regenerative braking force calculation means.
According to the above-described structure, it is possible to efficiently recover the automobile""s kinetic energy resulting from deceleration, i.e., deceleration energy, and use the recovered deceleration energy for operating the rotating electric machine as a motor, and thereby improve the operability, comfortableness, safety, and even fuel economy of the automobile.